1. Field of the Invention
This invention relates to a pay television system of using unidirectional television signals as in television broadcasting using a broadcasting satellite, and more particularly to a charging system of its receiving charge.
2. Description of the Prior Art
In a unidirectional signal transmisstion and receiving system as in a satellite television broadcasting, to collect a receiving charge at a terminal receiver as in the case of receiving a charged program of CATV, it is necessary to have the receiving charge paid by the subscribers on a "pay later" basis, and to disable the terminal receiver of the subscriber who does not pay.
This is practiced in a pay television of bidirettional CATV system.
In the case of CATV system, however, subscribers must apply for viewing a specivied pay television program to the transmission center by the up line of the bidirectional communication lines or by telephone, and such method cannot be employed in the unidirectional system such as satellite broadcasting. And in this method, when many subscribers apply for a same program at the same time to the center, an overflow of the capacity of the telephone line or overflow of the processing capacity at the receiving side occurred.
An example of such conventioanl composition is shown in FIG. 1, in which numeral 1 is a computer center of a CATV station for controlling the record of payment of receiving charge by the subscribers, selection of programs to be transmitted according to the request of the subscribers, compilation of control codes, and others while a CATV center 2 transmits the video signals prepared by VTR, film or at the studio according to its computer commands, together with said control codes. Reference number 3A is a head-end for signal transmission, and sends out plural television signals from the CATV center 2 in a form of, for example, mid-band television signals of VHF. Reference number 3B is a buffer circuit for receiving up signals from each receiving terminal, and the head-end 3A and tuner/converter 4 at the receiving terminal side of CATV and buffer circuit 3B are connected by a same cable or different cables. Or a telephone line may be used instead of the cable for up signal from the tuner/converter 4 to the buffer circuit 3B.
Numeral 4 is a terminal side tuner or converter for frequency conversion of mid-band signals into a first-channel (or second-channel) signals of VHF, and one channel is CATV signals of the mid-band is converted into one channel of VHF by the command from a key pad 5. Incidentally, when the CATV signal is scrambled, it is once converted into a base band signal, and descrambled, then converted into an RF signal again to be delivered as signal of one channel of VHF.
Numeral 6 is a television receiver for VHF band reception. The viewer applies for a desired program (charged) to the computer center 1 by operating the key pad 5 or through telephone set 7. At the center 1, the charge is set at every terminal. Or when sending out signals by scrambling, the descrambling key code is transmitted in the sequence of center computer 1, CATV center 2, head-end 3, and converter/tuner 4. At the tuner/converter 4, the received signals are descrambled by using this key code, and NTSC video signals of normal picture are reproduced, and are converted into one channel of VHF to be supplied into the television receiver 6. There are multiple tuners/converters 4 to telephone sets 7 which are terminal stations, and a central intervenes between the telephone set 7 and telephone interface 8. At the telephone interface 8, generally, an operator hears the request from each terminal, and it is converted into the format of input to the center computer 1. This is an example of the prior art.